defined in <a href="https://github.com/angular/angular/tree/2.0.0-alpha.34/modules/angular2/src/forms/model.ts#L165-L249">angular2/src/forms/model.ts (line 165)</a>
Defines a part of a form, of fixed length, that can contain other controls.
A ControlGroup aggregates the values and errors of each <a href='Control-class.html'><code>Control</code></a> in the group. Thus, if
one of the controls
in a group is invalid, the entire group is invalid. Similarly, if a control changes its value,
the entire group
changes as well.
`ControlGroup` is one of the three fundamental building blocks used to define forms in Angular,
along with
<a href='Control-class.html'><code>Control</code></a> and <a href='ControlArray-class.html'><code>ControlArray</code></a>. <a href='ControlArray-class.html'><code>ControlArray</code></a> can also contain other controls,